The invention relates to tamper-resistant valves for use on gas cylinders and to connection devices for use therewith.
Gas cylinders are vessels, typically but not necessarily of cylindrical shape, which are used for the storage of gas under a pressure, of at least 40 bar, and sometimes up to 300 bar, and typically in the range of 80 to 200 bar. The gas cylinder has a mouth which engages a valve closing the cylinder. The engagement usually of complementary screw-threads is required to prevent the elevated pressure within the cylinder from ejecting the valve. The valve has an internal configuration which enables the cylinder to be filled with gas and which enables gas to be supplied from the cylinder to a user. The valve is opened and closed manually.
Nitrous oxide is used in admixture with oxygen, typically as a 50/50 mixture, for short anaesthetic applications. It is extremely good, giving almost immediate pain relief, and flushes out of the body very quickly. In some countries the use of a pre-mixed gas is allowed, but in others, notably the USA, the use of pre-mixed gas is not permitted. In those circumstances, oxygen and nitrous oxide can be supplied separately and mixed on demand in a mixing device.
It is common for the nitrous oxide to be supplied in a pin index cylinder. In practice, however, it has been found that nitrous oxide supplied in this form is sometimes abused by staff, who could crack the valve open, and breathe the gas for “recreational” purposes. Also the gas can be stolen, and abused by people outside. The level of this abuse has been serious enough that the use of nitrous oxide has been discontinued in many establishments.